1. Field of the Invention
The present invention relates to an apparatus for stacking, bundling and transporting a stream of sheets, such as printed sheets, in signature form. The invention more particularly relates to a vertical stacking machine which stacks the stream of signatures and then compresses, clamps and straps the signatures into a bundle for transportation and delivery.
2. Description of the Prior Art
In the printing industry it is necessary to quickly handle printed sheets as they exit the high speed printing presses which are in common use today. The presses deliver printed sheets onto conveyors in serial, shingled form which then must be stacked into large bundles for delivery to a customer. Sheet stacking devices are commonly used for handling sheets as they are delivered from printing presses.
Printed sheet material is commonly delivered to a stacking machine in the form of folded sheet signatures which will be assembled to form a completed magazine or book. Vertical stackers are well known in the art as exemplified by U.S. Pat. Nos. 3,739,924; 3,825,134; 4,772,169; 4,953,845 and 5,215,428, which are incorporated herein by reference. Features common to prior art stackers are that they receive printed sheets, assemble them into a vertical stack and compress the stack from the top to remove entrained air. As used herein, "vertical" includes a stack which may be formed at any angle including those from true vertical to about 45.degree. from true vertical. In virtually all vertical stackers in use today, a stack is actually formed at a slight angle to true vertical.
After a stack of sheets is formed, it must be compressed, strapped into a bundle and transported away from the stacker for other operations. The industry has evolved such that stacking equipment can rapidly collect, stack, compress and bundle sheets at the speed they are produced by the printing press.
It has been desirable to employ high speed strapping equipment which automatically or semi-automatically ties the compressed stack into a bundle. In this regard, it is necessary to prevent the bundles from becoming disarranged during compressing and strapping. This avoids damage to the sheets by downstream machinery. It has therefore become common to clamp the stack along its sides during compression and strapping to prevent the sheets from drifting out of the stack during strapping. One or more clamps are initially positioned out of the path of the stack and, at the appropriate time, they are driven into the path of the stack at one side or opposite sides thereof and hold the stack sides. The clamps may engage either simultaneously or sequentially and advance until either the stack or a stop is reached. After strapping, the clamps retract and the bundle is transported away for the next operation. A problem in the art is that currently used clamps obstruct strapping equipment. This has necessitated the use of expensive, custom made strapping equipment in order to avoid these obstacles. According to the present invention, a stacking machine is provided which has an improved clamping mechanism. The inventive clamps comprise one or more and preferably a pair of opposing bars attached to the driving mechanisms in a cantilevered fashion. That is, connecting rods are attached to each bar only at the top and/or the center portion of the bar. The opposite, bottom end of each bar is free of attachment to the connecting rods and driving means. As a result, a critical obstruction is removed. This frees crucial space and allows the use of much less expensive strapping equipment which is common in the printing industry.
An important feature of the present invention is to provide an automated system for receiving, stacking, clamping, compressing and transporting sheets, which has an improved cantilevered clamping means which can be readily and easily positioned on and removed from the stack of sheets. The clamp of the present invention operates such that when the bundle is compressed and the clamp is positioned in tight contact with the opposite sides of the bundle, the clamp will automatically hold in that position until the bundle is strapped after which the clamp releases when the clamped bundle is finally positioned for transportation. These and other objects and advantages of the invention will become apparent upon a consideration of the following detailed description.